mailcow-dockerized/data/conf/postfix/config_templates/mysql_relay_recipient_maps.cf.j2

user = {{ DBUSER }}
password = {{ DBPASS }}
hosts = unix:/var/run/mysqld/mysqld.sock
dbname = {{ DBNAME }}
query = SELECT DISTINCT
  CASE WHEN '%d' IN (
    SELECT domain FROM domain
      WHERE relay_all_recipients=1
        AND domain='%d'
        AND backupmx=1
  )
  THEN '%s' ELSE (
    SELECT goto FROM alias WHERE address='%s' AND active='1'
  )
  END AS result;